ci: Prevent duplicate CI runs

https://github.com/orgs/community/discussions/26276
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 82bf6af..c2b4e02 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,10 +5,12 @@
 name: ci
 
 on:
-    push:
-    pull_request:
-        branches:
-            - main
+  push:
+    branches:
+    - main
+  pull_request:
+    branches:
+    - main
 
 env:
   CMAKE_GENERATOR: Ninja